Abseiling is a technique which is used to descend steep surfaces such as cliff faces and is often used by persons involved in activities such as mountain climbing, canyoning and caving. In order to abseil down a cliff face, one end of a rope is made fast at the top of the cliff and the person making the descent then slides down the rope. The rope is passed either around the body of the person or, more usually, through a descender attached to a harness worn by the person such that the passage of the rope around the body or through the descender provides sufficient friction to slow the rate of descent to a safe speed. These techniques are also used in the workplace e.g. by persons working at heights on roofs and buildings, and by rescue services.
A descender defines rope engaging services around and between which the rope travels along a tortuous path, to provide frictional engagement between the rope and the descender. The rate of descent is normally controlled by holding the free or tail end of the rope to control the tension on the rope where it emerges from the descender thereby to control the degree of friction engagement between the rope and descender, which in turn controls the rate of descent.
Descenders used in abseiling vary greatly in performance and complexity, there being a variety of relatively simple devices which rely on frictional engagement between the rope and metal rings or racks about which the rope is wrapped, and a number of more complex descenders which incorporate a braking mechanism which allows friction between the rope and descender to be varied other than by simply controlling the free or tail end of the rope. The earliest of these more complex devices have a handle or lever which, when operated, tended to increase the friction between the descender and the rope. This type of descender had the problem that the brake was not self-engaging and therefore, if the user was knocked unconscious, he or she would fall in the same way as a user of the earlier devices.
A number of devices now include automatic braking mechanisms in which a handle is operated by a person using descender to control their speed of descent and if the handle is released, a brake actuates and prevents a user falling uncontrollably. Such a descender is disclosed in U.S. Pat. No. 4,596,314.
It is known to provide a descender having a sheave around which a rope passes located between front and rear plates which pivot to open the descender to allow a rope to be threaded through. The sheave may be shaped and pivotable to control the resistance to the passage of the rope. One disadvantage to such descenders is that if the plates pivot open during use, the possibility exists that the descender could fall off the rope, if the plates are not locked in a closed position.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.